The present invention relates to a method for automatically activating freewheeling in a vehicle.
Automatic transmissions of the Automated Mechanical Transmission (AMT) type have become increasingly common in heavy-duty vehicles as microcomputer technology has continued to advance and has made it possible, with a control computer and a number of control elements, for example servo motors, to precision control the engine speed, the connection and disconnection of an automated clutch between engine and gearbox and clutch members of the gearbox, relative to one another, so that smooth gear shifting is always obtained at the correct rev speed. The advantage with this type of automatic transmission compared to a traditional automatic transmission based on a set of planetary gears and with a hydrodynamic torque converter on the input side is firstly that, particularly as regards use in heavy vehicles, it is simpler and more robust and can be produced at substantially lower cost, and secondly that it has higher efficiency, which means the prospect of lower fuel consumption.
A traditional automatic transmission based on a set of planetary gears may have one-way clutches between the planetary gear sets, which transmit torque from the engine to the wheels when the wheels are driven by the engine, but which, when torque is transmitted in the opposite direction (i.e. at zero throttle and with the vehicle in motion) disengage and cause the vehicle to freewheel without engine braking, which, by utilizing the kinetic energy of the vehicle, yields lower fuel consumption than if the engine is braking.
A corresponding freewheel function for automated mechanical transmissions is shown by WO02/092378. Here, a freewheel function is obtained by putting a splitter gear disposed in the gearbox into its neutral position when an accelerator pedal (gas pedal) disposed in the vehicle is located within a predetermined swivel angle range, which starts at a distance from the rest position of the pedal and extends over a slight angle within the total swivel angle of the pedal. When the driver wishes to change the driving condition from driving engine to allowing the vehicle to freewheel without engine braking, he lets up on the accelerator pedal so that it reaches the predetermined range when the drive from the engine is broken. If engine braking is required, he further releases the gas pedal, either fully or, in any event, to the point where it passes through the predetermined range within which disengagement occurs.
When a vehicle is equipped with an auxiliary brake, such as an engine brake, for example an exhaust gas pressure regulator or compression brake, or a hydraulic or electric retarder, this type of brake is often used when the vehicle is coasting. The inclination of the downhill slope can sometimes vary and if the driver wants to hold a certain vehicle speed through the whole varied down slope he often uses the auxiliary brake to hold the vehicle speed and to save the service brakes. This means that if the downhill slope varies the driver may have to repeatedly engage and disengage the auxiliary brake, or adjust it between different braking power levels and even turn the auxiliary brake to the off position at times, for example if the inclination of the downhill slope becomes relatively small.
Many times, a situation occurs just after disengagement of the auxiliary brake when freewheeling would be advantageous because at a minimum, it would save fuel. According to known techniques, in order to activate the freewheel function just after disengagement of the auxiliary braking power the driver has to press the accelerator pedal slightly (i.e. within said predetermined swivel angle range, see WO02/092378) and then, as soon as possible, release the accelerator pedal. This is counterintuitive and unnatural for the driver to have to press the accelerator pedal for freewheel activation when traveling downhill and the driver desires to hold a certain vehicle speed.
An object of the present invention is therefore to improve the procedure and eliminate the unnatural feeling of having to press the accelerator pedal for activating the freewheel function just after the auxiliary brake has been deactivated. Another object is to improve fuel economy.
The method according to the present invention is a method for activating a freewheel function of a vehicle, where the vehicle is equipped with an auxiliary brake. An auxiliary brake control is included for controlling the braking power of the auxiliary brake by positioning the auxiliary brake control between an auxiliary brake “not-active” position and at least one auxiliary brake “active” position. The method is characterized in that when deactivation of the auxiliary brake occurs due to manual positioning of the auxiliary brake control to the auxiliary brake not-active position, the freewheel function is automatically activated if freewheeling condition is sensed.
The advantage with the method according to the invention is that the driver would not need to press the accelerator pedal slightly and then as soon as possible release the accelerator pedal to activate freewheeling. The handling of the vehicle will be simplified and fuel consumption will be decreased due to the automatic freewheel activation according to the invention.
According to one aspect of a method according to the invention, the sensed freewheeling condition includes at least sensing that an accelerator pedal for controlling the driving torque of an engine in the vehicle is released and that a brake pedal for controlling service brakes in the vehicle is also released. This gives a natural procedure for the driver to activate the freewheeling function just by positioning the auxiliary brake control in the auxiliary brake not-active position and not touching the accelerator pedal and brake pedal.